CT Glass
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Acoustic Laminated

CT Glass offer a range of laminated and toughened laminated glasses incorporating a special acoustic interlayer by TROSIFOL. Trosifol® Sound Control has all the outstanding security properties of standard laminated glass, as well as high sound insulation values, up to 2 dB better than float glass of the same thickness.

Noise is unwanted sound, this may be from a variety of sources from road traffic to factories to aircraft. Analysis of the most common source, traffic noise;, has been available for many years and is well understood. British Standard 8233:1987 sets out the acceptable internal noise levels for different room types within different types of buildings.

The critical elements when considering noise are –

  • Source – most noises are not a single frequency but a wide range of frequencies
  • Loudness – the sound pressure level (dB or dBA)
  • Time – length of exposure as well as time of day

Sound is measured across a range of 16 frequencies called thirdoctave bands. The frequency, (cycles per second), determines the pitch and is measured in hertz (Hz). Six “octave” bands are usually sufficient to detail sound levels, required reduction or acoustic performance. They are –

125Hz 250Hz 500Hz 1000Hz 2000Hz 4000Hz

Loudness is measured in decibels (dB). The threshold of hearing is 0 dB whilst 120 dB is the threshold for causing physical pain. The human ear does not hear in a linear scale but by one which is related to relative changes (logarithmic). As such a change of +/- 3 dB is barely perceptible. A change of +/- 5dB is clearly noticeable and a change of +/- 10 dB is twice or half as loud.

The term dBA refers to A-weighted decibels where a specific adjustment has been made to take into account the response of the human ear.

These are two methods of checking the acoustic performance, firstly specifications for major projects will often detail the sound reduction requirements for the above frequencies. It is then necessary to conduct research to find a glazing solution that will meet this specification.

The simplest and most accepted method for proving compliance is the use of one of the commonly quoted indices that use a single value. The most frequently quoted are –

  • RW (weighted reduction), defined by BS 5821:1984, it incorporates a correction for the ear’s response.
  • RTRA* (traffic noise reduction), measured in A-weighted decibels (dBA). Because it is based on traffic noise, it gives good guidance to actual performance. Importantly, and specific to this index, internal requirements can be subtracted from external noise levels to determine the necessary performance.

* Two new indices are also becoming common which are equivalent to Rtra – C and Ctr..

C – Corresponds to high speed traffic noise i.e. motorways
Ctr –Corresponds to low speed traffic noise i.e.urban areas.

All glazing reduces the passage of sound and the term “acoustic glazing” tends to refer to glazing that has been deliberately chosen for its acoustic performance.

Single glazing is surprisingly good at reducing noise transmission when compared with basic double glazing. This is due to the fact that every thickness of glass has its own critical frequency at which it resonates, with two or more panes resonating together this can result in a sharp drop in performance through Coincidence Resonance.